1. Field of the Art
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device with a recess of an insulating layer filled with wiring material.
2. Prior Art
As elements formed in a semiconductor device become fine, a contact hole formed in an insulating layer also becomes fine. It is accordingly difficult to reliably form an Al film within a contact hole. The reason for this is that the step coverage of an Al film to the contact hole is poor so that the Al film becomes too thin at the side walls of a contact hole.
To solve the above problem, there has been proposed a method whereby an Al film is deposited on an insulating layer to fill a contact hole with the Al film, the Al film on the insulating layer is etched back with the Al film within the contact hole remaining unetched, and then a wiring Al film is deposited. According to this method, since almost all space within the contact hole is filled with Al, there is no problem of a poor step coverage.
The above conventional etch-back method will be detailed with reference to FIGS. 6A and 6B. The semiconductor device shown in FIGS. 6A and 6B has a barrier layer made of titanium nitride film or the like which is formed prior to filling an Al film, in order to avoid possible junction breakage.
Referring to FIG. 6A, a semiconductor substrate 1 is formed with specific regions 2a and 2b such as source, drain or the like to which an Al wiring is to be connected. An insulating layer 3 formed on the semiconductor substrate 1 has contact holes 3a and 3b formed above the specific regions 2a and 2b. The contact holes 3a and 3b are deposited with a barrier layer 4 for avoiding possible junction breakage. An Al film 5 is deposited on the entire surface of the barrier layer 4 to fill the Al film within the contact holes 3a and 3b. The Al film 5 thus formed will have indentations 5a and 5b because of the presence of the contact holes 3a and 3b. The depths of the indentations 5a and 5b are dependent on the cross sectional areas of the contact holes 3a and 3b. After etching back the Al film 5, Al remains within the contact holes 3a and 3b as shown in FIG. 6B. The indentations 5a and 5b are transformed into indentations 5a' and 5b' on the Al films 5 left within the contact holes, because of isotropic etching. The quantities of the Al films 5 left within the contact holes 3a and 3b are respectively dependent on the cross sectional areas of the contact holes, and there is a large difference between the indentations 5a' and 5b'. Therefore, even if another Al film is deposited on the Al-films 5 left within the contact holes, electrical contact between the new and old Al films may not be given. Such case occurs not only for contact holes but also for various recesses such as wiring trenches.
FIG. 7 shows another example of a semiconductor device manufactured in accordance with the abovedescribed conventional method. As seen from FIG. 7, a contact hole (or wiring trench) 3a (3c) of an interlayer insulating film 3 on a semiconductor substrate 1 is filled with an Al film. After etching, an Al film 5A remains unetched. If another interlayer film 10 is deposited after a wiring Al film 7 is deposited, a cavity 10a becomes present in some cases as shown in FIG. 7.
As described above, according to the conventional method, a wiring material filled within a recess such as a contact hole is etched back. The etched-back surface of the wiring material within the recess has an indentation so that if another wiring material is deposited on the remaining wiring material within the recess, both the materials may not reliably contact each other, or if another interlayer insulating film is deposited on the other wiring material, a cavity may be formed.